There are sorbent materials, such as lime and limestone, which are conventionally used in scrubbers to remove SO.sub.2 from gases. In one modification, an example of which is disclosed in U.S. Pat. No. 4,612,175, a metal chelating agent is added to the scrubber slurry, which promotes absorption of NO.sub.x. The NO.sub.x is converted to HNO.sub.2 and HNO.sub.3 and at least some of the SO.sub.2 is converted to HSO.sub.3.sup.31 . Once in solution, the HNO.sub.2 and HSO.sub.3.sup.31 form hydroxylaminedisulfonate (HON(SO.sub.3 3H).sub.2, abbreviated HADS) and related compounds. However, an accumulation of the HADS compounds in the scrubber slurry causes problems in that it interferes with the disposal of process waters and solids and with the process chemistry. The problems are compounded in that HADS should be treated prior to disposal so as not to create an environmental problem.
An object of the present invention is thus to provide a method for removing NO.sub.x /SO.sub.2 from combustion gases using a metal chelate, while also during this process, converting NO.sub.x to a species which can be thermally reduced to nitrogen gas.
This and other objects of the invention will be apparent from the following description and from practice of the invention.